Make sure git-stash works from subdirectory.

We say "SUBDIRECTORY_OK" but we did not chdir to toplevel; this
is fine as long as everything we use can be started from a
subdirectory, but unfortunately "merge-recursive" is not one of
the programs you can safely use from a subdirectory.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3903-stash.sh

@@ -66,4 +66,11 @@ test_expect_success 'apply stashed changes (including index)' '
 	test 1 = $(git show HEAD:file)
 '
 
+test_expect_success 'unstashing in a subdirectory' '
+	git reset --hard HEAD &&
+	mkdir subdir &&
+	cd subdir &&
+	git stash apply
+'
+
 test_done